Electron tubes are evacuated by pumping systems specifically suited for the respective production process. Glass-covered tubes are, as a rule, connected to the pumping systems by glass tubes. These glass tubes, called pumping leads in technical terminology, are severed from the pumping system after the evacuation through ablation or melt-down. The portion of the pump lead facing the tube remains a component of the tube base upon which the internal components of the tube are installed. For large scale series manufacture, a device is used for the ablation process which is designated as a seal-off unit.
The seal-off unit consists of several parts which, until now, were assembled in axial direction to correspond with the drawing in FIG. 1. In the configuration of FIG. 1, an electron tube 1 is evacuated by a pumping system 2. The connection between the electron tube and the pumping system is formed by a tubularly-shaped component 4 which is called the pump lead-in or exhaust tube. In order to make the conductance in the pump lead-in or exhaust tube as large as possible and to thus limit the pump-down time to a minimum, the lead-in tube must be as short as possible. This means that the electron tube base 16 and the pumping system 2 must be disposed closely together. The sealing-off unit 5 is located between the electron tube base 16 and the pumping system 2. It consists of a housing 6 with cover 8, various installation elements 9, 10, 11 and heating coil 6.
The sealing-off unit must be disassembled if it is desired to replace the heating coil. This occurs in axial direction after disconnecting the bolts 12. The close axial construction and attachments 3, which is necessary for reasons mentioned above, with the attachment 3 being required for handling the electron tube and its components during the pump-down process, make the disassembly extremely complicated and time consuming.
The heating coil is a part which is exposed to high thermal loading and thus considerable wear. This postulates frequent replacement of this component. The replacement of these components and other maintenance processes are a considerable burden involving effort and time in case of mass production. A rapid and rational progress of this manufacturing process is to be aimed at. This could be only unsatisfactorily solved with the conventional designs as has been demonstrated above.